Document: JON-3-88-2

Contingency and predictability in wetland communities: Effects of environment, history, and spatial scale.

CHASE, J.M.*

University of Pittsburgh, Pittsburgh, PA 15260 USA ¹

Abstract:
Much of ecological theory is based on the assumption that a single attractor known as an equilibrium or climax governs community structure. Alternatively, natural communities exhibit a wide variety of states, even under seemingly identical environmental conditions. Furthermore, some theories predict that communities can exhibit multiple stable states that depend on historical contingency. Nevertheless, historical contingency does not preclude predictability. I present a theoretical analysis that predicts: 1) Local communities with higher resource supply (i.e., primary productivity) should be more historically contingent, and thus more divergent from one another than those with lower resource supply, 2) more disturbed communities should be less contingent than less disturbed communities, 3) local communities with higher spatial connectance should be less contingent than those with lower spatial connectance. These predictions are upheld in experiments and pattern-analyses in wetland communities. Finally, these predictions help to explain a variety of observations in natural communities, such as the scale-dependence often observed in the productivity-diversity relationship. Local productivity-diversity relationships can be 'hump-shaped' while regional relationships are monotonic, because local community divergence (i.e., differential composition among local sites; beta-diversity) increases with productivity.

Keywords: Community assembly, Multiple stable states

This abstract is being presented at: 9:45 AM in session:
Oral Session #39: Theoretical Ecology.